The present invention relates to an analyzing apparatus and an analyzing method for performing the measurement of optical and electrical characteristics of materials employing the spectroscopic method, and in particular, it relates to an analyzing apparatus and an analyzing method for material measurement in non-destructive and non-contacting way without necessitating the use of any reference.
Time-domain spectroscopic method in the terahertz-wave region (100 GHz to 20 THz) is a spectroscopic method having a feature of direct measurement capability for the complex optical constants such as complex refractive index comprised of refractive index and extinction coefficient of material in this frequency region, the complex electrical conductivity, or the complex dielectric constant without requiring the Kramers-Kronig transformation or the like. Furthermore, from the complex optical constants in the terahertz-wave region, various information on solid, liquid, or gas phase materials, which are difficult to obtain from measurement in other frequency ranges, can be obtained. Furthermore, non-destructive and non-contacting measurements of the complex optical constants are possible. From such background as mentioned above, research and development of time-domain spectroscopy in the terahertz-wave region and material research using it are pursued energetically.
While a lot of researches employing the terahertz time-domain spectroscopy have been implemented on solid, liquid and gas phase materials, many of them were conducted on the transmittance measurement of the terahertz electromagnetic wave. In some of other conventional researches, reflected electromagnetic wave from a sample was measured in order to derive the optical constant of the sample having a small terahertz electromagnetic wave transmittance.
Outline of the time-domain spectroscopy in accordance with a transmittance measurement of a prior art 1 is explained referring to FIG. 5. In the time-domain spectroscopy of the prior art 1, both of electromagnetic wave transmitting through a sample and electromagnetic wave without placing the sample (reference data) are measured.
FIG. 5 is an outline drawing of a time-domain spectroscopy of prior art 1. A pulse laser 100 generates an optical laser pulse 101. A beam splitter 102 divides input optical laser pulse 101 into optical laser pulses 103 and 104, and outputs them. The optical laser pulse 103 is used for radiating electromagnetic wave while the optical laser pulse 104 is used for triggering an electromagnetic wave detection photoconductive device 110. The optical laser pulse 103 is incident via a mirror 120, a chopper 105, and a lens 106 onto a radiation antenna 108 that is a terahertz electromagnetic wave radiation photoconductive device.
The radiation antenna 108 radiates terahertz electromagnetic wave 124 by inputting the optical laser pulse 103. The terahertz-wave 124 generated is collimated by a hemispherical lens 122 and a parabolic mirror 107 and is incident on a sample 109. A stabilized power supply 121 feeds electric power to the radiation antenna 108.
A chopper 105 is a rotating device having opened sector parts and closed sector parts alternatively, and it repeats transmission and interruption of the laser pulse 103 at a period of 1 to 3 kHz.
Terahertz electromagnetic wave 125 passing through the sample 109 is condensed by a parabolic mirror 113 and a hemispherical lens 123, and incident on a receiving antenna 110 that is a terahertz electromagnetic wave detection photoconductive device placed at a position symmetric to the position of the radiation antenna 108. The receiving antenna 110 that is a detecting device outputs a signal that is proportional to electric field of the teraheretz electromagnetic wave applied at an instant of excitation by femto-second laser pulse 104.
The other laser pulse 104 divided at the beam splitter 102 is inputted to the receiving antenna 110 via a retro-reflector 111 forming a reflecting mirror, a mirrors 128, 129, and lens 130. By moving a movable stage 112 on which the retro-reflector 111 is fixed in the direction indicated by arrows, timing (amount of time-delay of illumination timing) at which the laser pulse 104 excites the receiving antenna 110 can be changed. A current amplifier 126 amplifies the output signal from the receiving antenna 110. A lock-in amplifier 127 inputs an output signal of the current amplifier 126 and a rotation control signal (or rotation detection signal) of the chopper 105, and then take out component corresponding to the rotation of chopper 105 from among the output signal of the current amplifier 126.
While changing the amount of time-delay by moving the movable stage 112, amplitudes of the output signal (electric field of terehertz electromagnetic wave) from the lock-in amplifier 127 at respective delay-time are measured. As a result, time-resolved waveform of radiated terehertz electromagnetic wave as shown in FIG. 6 (amplitude/amount of time-delay characteristics of electric field) can be measured.
As has been described above, the time-resolved waveforms themselves of terhertz electromagnetic wave, that is, amplitude/phase characteristics of electromagnetic wave can be measured. Measuring the time-resolved waveforms for the case of inserting the sample in the path of electromagnetic wave and for the case of not inserting it, respectively, then taking a ratio between complex spectra resulted respectively from respective Fourier transformations, the complex transmittance spectrum of the sample is obtained. Thereby, complex optical constants such as complex refractive index or the complex electric conductivity of the sample can be obtained all at once over a wide range of terahertz-wave region.
In the time-domain spectroscopy of a prior art 2, measuring a time-resolved waveform of electromagnetic wave reflected from the surface of a sample of the measuring objective and a time-resolved waveform of electromagnetic wave reflected from the surface of a material (reference) serving as the reference whose reflectance is known to be 1, and then taking a ratio between their complex spectra, the complex reflectance spectrum of the sample is obtained.
While in the prior art 1 the transmitted light through a sample is measured, in a prior art 2 the reflected light from a sample is measured. On the rest of the above point, they have the same configuration.
In the time-domain spectroscopy of the prior art 2 utilizing the reflected light, however, in order to know the phase information with an ample accuracy, it is necessary to make matching between the positions of the reflecting surfaces of a sample and a reference within an accuracy less than several micrometers (T. I. Jeon and D. Grischkowsky: Applied Physics Letters, Vol.72, 3032-3035 (1998)). This is very difficult to achieve with a mechanical accuracy of ordinary sample holders. In order to avoid this difficulty, a novel method is developed, in which, a transparent material of known film thickness and known refractive index onto the surface of the sample is attached, both of reflected electromagnetic wave at the surface of the transparent film and reflected electromagnetic wave at the interface between the transparent film and the sample are measured, and by performing data processing taking the film thickness and the refractive index of the transparent film into account, an enough accuracy is obtained (Shigeki Najima et al., 2001 (Heisei 13) 61st Applied Physics Autumn Academic Conference). However, this method has a problem that a certain processing step onto the sample is necessary and the data processing includes vexatious complexity.
In the time-domain spectroscopy utilizing the reflected light, trial of obtaining the optical constants without performing any measurement on a reference is also attempted. A method is proposed, in which, while changing the incident angle onto the sample, the Brewster angle is obtained by measuring the reflected waveform, and then from those data, the refractive index of a thin film on a substrate, that is a sample, is obtained (M. Li et al.: Applied Physics Letters, Vol. 74, 2113-2114 (1999)). Although this method is excellent in enabling the measurement of the optical constant of extremely thin film, it is necessary to move the position of a receiving antenna at each time when the incident angle is changed. In the time-domain spectroscopy, as it is necessary to adjust the light path of a femto-second pulse laser triggering the receiving antenna at each time when the incident angle is changed, it requires a vast time and effort in measurement, which makes the method unpractical. Moreover, by this proposed method, continuous spectrum cannot be obtained.